The present invention relates to an antenna device for an automobile which is installed in the automobile body.
A conventional antenna device, for example, is disclosed in Japanese Kokai No. 62-17920. The conventional device integrates an antenna mast for an AM/FM radio receiver and another antenna mast for an automobile telephone. The telephone antenna mast, which transmits and receives shorter wave lengths than the antenna mast for a radio receiver, is located close to an automobile body. The automobile body is equivalent to a grounded plate. Therefore, the telephone antenna mast may be affected by the automobile body if the telephone antenna mast is close to the automobile body. As a result of this, the most sensitive direction of the telephone antenna mast is not directed horizontally. Therefore, the telephone antenna mast may be less sensitive.
In order to solve the above drawback, the telephone antenna mast may be located away from the automobile body 1. Such an antenna device is disclosed in Japanese Kokai No. 64-77205. In such an antenna device, as shown in FIG. 6 of the present application, the telephone antenna mast 1 is fixed onto the top of the radio antenna mast 2 in order to locate the telephone antenna mast 1 away from the automobile body 3. The telephone antenna mast 1 is electrically connected to an automobile telephone unit 5 via coaxial cable 4.
The coaxial cable 4 has to be thinner than the AM/FM antenna mast 2 since the coaxial cable 4 is inserted in the AM/FM antenna mast 2. The coaxial cable 4 has a feeder conductor 4a and a shielded conductor which surrounds the feeder conductor. Thus, in the conventional antenna device, the coaxial cable 4 has a large transmissive loss since the feeder conductor has to be very thin.